Evening
First off I’m gutted for you. I know how much you love that 5 series and if you like a car that much and it’s not ‘good’ it’s sh1te
It’s easy to say do this or do that re the garage- but reading that account from your view it would appear they didn’t really want to do the job?
Have...
Prise the tweeter off and disconnect
Take the door card off
Undo the 3xt30 Torx that hold the mirror on
Once off the car take the glass out by rotating the ring that holds the mirror onto the moving table it sits on
Once that’s off you will see the 7-8 small Torx (t15 from memory but may be...
If it’s an m54 yes the rubber boot that runs from the airbox to the intake
They split for fun especially around the convoluted part
What code? I’m betting it’s running lean
Check for air leaks especially where there are idle issues on start up
How is the elbow from the intake as that’s the usual spot for holes letting more air in
It shouldn’t take any
May be worth resetting the throttle adaptations
Depress accelerator
Turn ign on
Wait 30 sec
Turn ign off
Wait 30 sec
Release accelerator
If you put a cluster in that isn’t native to the car it will throw a mileage tamper dot which will disappear when resolved
If that ‘fixes’ the issue you can then either implant your eeprom chip into the new cluster or recode it